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damn it, whats my problem?

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. So long story short.


Truck is a 2wd 720 L20 5 speed


Past month when taking off from stand still there has been a metal creaking noise that seemed to come out of the tranny. Then it started to continue to do that after I shifted into second. Last week the creaking turned more into a straining noise, then I started hearing pieces of metal rolling around and my truck started running very rough over 30, lots of vibration. I felt a lot through my shifter


Seemed like a tranny issue, so put a different one in, and still have most of the problem. No metal rattling atleast, but a small creak when accelerating from a stand still.


What would make my truck run like a bad u joint, but isn't a u joint? Its new so I know its not that.

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Bad motor mount. A bad tranny mount is more likely but the tranny change would have /should have turned that up.


My pick:

Driveshaft center bearing rubber isolator (not the bearing they don't go bad, just the rubber rots ) ...but again this would have to come off to change the transmission and should have been noticed.



The exhaust pipe on the 720 has a support that bolts to the back of the tranny so it, or the exhaust pipe could be loose or the pipe in the muffler/converter could be loose and sliding back and forth making weird noises.


Get under and pull and tug on all the pipes and see if anything hits the body or frame.

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Who installed the tranny?

Did they check the clutch cover and disc?

If a pilot bearing goes bad, the front of the tranny imput shaft can move around causing hard shifting, grinding, and it can destroy the front bearings eventually.

Also the throwout bearing can cause squealing, vibration, and hard shifting.

Did it make any noise at an idle clutch pedal out, or pushed in?

Have you lowered the truck lately?

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The swap was done by a local retired mechanic. Whom also has the largest amount of datsun

parts I've seen in one spot.


When the clutch is in no noises at all, and no noise when not accelerating. Right now there is no squealing, just a minor metallic creak. Which seemed to have stopped by the time I got home, however the roughness feels like its coming from the rear. The vibration only happens when accelerating. Just like a u joint.


I don't have any exhaust past the converter.


3 inch drop done by pumpkn210 last summer.


Tomorrow I will spend the morning knocking around. Could this be coming from the rear diff?


Would I be able to check the bearings myself? I'm at an "advanced tinkering" level as far as mechanics.


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Lowering will throw the drive line angles out and cause vibration and at the same time accelerate U joint wear. If still vibrating I would inspect the driveshaft more.

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I forgot to mention clutch is new. I can't wiggle anything, my driveshaft is very tight.


How would I go about checking my bearings?


The roughness feels like some sort of drag from the rear so I have a lot of pics of it.












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I know! I read it like that too, but I do all of this from my phone so I shorten a lot of sentences!


Atleast we aren't talking about polishing a shaft.


If I were using a comp I'm very articulate, and would answer all of the questions you guys are asking me a little better.





I was like??? Then :lol:

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It the d/s damaged? Dinged or bent? What's that mossy looking shit I see near thew gas tank? You bottom out on anything?


Raise one wheel and put in neutral. Spin the tire and watch the d/s for wobble.

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He lives on a mountain and some crap got under there. I didn't see it till I went to take a pic.


Good tip mike I will try that in the morning.


It the d/s damaged? Dinged or bent? What's that mossy looking shit I see near thew gas tank? You bottom out on anything?


Raise one wheel and put in neutral. Spin the tire and watch the d/s for wobble.

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this sounds early familair like when I lost the pinion bearing in my mazda and grenaded the spiders .....or the carrier bearing mine made noise after the new rear end and i replaced the carrier and all better ...i threw u joints in her to for safe measure....i like the isolater suggestion too though it would only take a little deflection in the d/s to make horrible things happen..dont continue to drive if it is it will waste other parts of drive train...mainly the u joints...


me personally, I think bottoming out caused a issue with d/s... since it looks like u drug the pumpkin...draggin a rear end will mis-align things easliy causing this issue...easiest take u bolts off , re pin rearend and re install u bolts....hopefully addressing issue...

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I'm on my second u joint in a year, both brand new out of the box. Last time I thought it wasn't my u joint it was, but when the tranny got changed the u joint was checked.

Could be cause by bottoming out, but the metal noise I've been hear, and it didn't run rough like this until immediately after I heard a piece of metal come loose and was shaking around in what I assumed was my transmission. Now I'm not sure.





I got called in today so nothing I can do about the truck until I can get some relief at work this week.

Then I will put it up and see what happens with my d/s

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^True that. Should flop over freely when rotated. Shouldn't have excess slop however. A lot of people just put in joints without checking the play, thus they're tight and blow out and cause issues. Or they're sloppy and cause issues. If you didn't put them in yourself, remove the driveline and feel the bearings. (Oh baby! ;) )

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  • 2 months later...

i am not sure if the 720s ran a 2pc drive shaft but my new truck was lowered and made ALOT of noise and massive vibration on acceleration in 1st gear. i raised the carrier bearing, which i need to change as the isolator is SHOT, an inch and that all went away.now to do the U-Joints and replace the output shaft seal.

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